The present invention relates to user interfaces for measuring waveform distortions, and more particularly to adjustable electronic graticules for measuring waveform distortions to eliminate parallax errors and to eliminate the need for interpolation between fixed graticule marks.
A waveform monitor is a specialized form of an oscilloscope for making measurements of video waveforms in the television industry. Graticules generally are found in two forms on a cathode ray tube (CRT) used for waveform monitoring: internal fixed graticules on the CRT; and plastic overlays with fixed graticules for placing over the face of the CRT. Internal graticules only contain commonly used markings, while graticules for special measurements, such as waveform distortions, are relegated to plastic overlays to reduce the clutter for normal operation. In addition these external overlays come in two forms; one for normal viewing and one slightly reduced for photographic uses.
Some common television measurements performed using these special purpose graticules include K-Factor, ICPM (Incidental Carrier Phase Modulation) and short time distortion (SD). K-Factor measurements include the use of a submarine-shaped graticule to measure the distortion of a sine-squared pulse which generally has markings for two and five percent distortion values, with other values of distortion being interpolated visually by an operator from these values. ICPM graticules have straight lines extending radially outward from a zero carrier reference point, usually in the form of a family of markings spaced in two degree intervals. SD measurements require a complex graticule to measure the distortion of a sine-squared step waveform. Each video standard, such as NTSC, PAL, SECAM and the like, has its own definition of distortions and graticule shapes to measure these distortions, often resulting in the requirement for different graticules for each video standard for the same measurement.
As is readily apparent these external graticules are subject to parallax errors when used by an operator, as well as interpolation errors when the waveform falls between fixed graticule locations. What is desired are adjustable electronic graticules for measuring waveform distortions that do not clutter the screen when the measurement is not desired, yet when used eliminate parallax and interpolation errors to provide a more accurate measurement of the waveform distortions.